Calculating a Viral Index

It is important to understand how viral your app is. The viral index (also know as ‘k factor’) is the numeric representation of how spreadable your app is in viral channels like Facebook, Twitter, and email.

To understand these calculations, you should first read our article on the anatomy of the viral loop.

The viral loop consists of two halves, we call these the In-Channel and In-App sections.

The In-Channel Section

This consists of the See and Click sections of the viral loop. This means the user must first see a viral object in the channel (eg. Facebook Newsfeed, Twitter stream,  or email inbox). Secondly, the object must be compelling enough to convince the user to click in and go to your application.

The important metric with this side of the viral loop is click-rate. Click rate is defined as the average number of clicks each object receives. In the Facebook Newsfeed, posts tend to receive between 0.5-5 clicks/post and therefor have a click-rate between 0.5-5.

Your goal as a developer is to create content that is novel, interesting and encourages clicking. You also must choose channels that are more effective. For example: The Facebook Requests channel has been heavily spammed by many developers and many users don’t ever look at their Application Requests. If users never even see your viral objects, it doesn’t matter how compelling your content is.

The In-App Section

Consists of the Desire to Share and Share sections of the Viral loop. In this section, the user is in your application, and your primary viral objective is to convince and allow 100% of your users to share viral objects.

You can’t force users to share, so you must create content that they badly need to share. Read Why do people share? for insights on how to do this. Once users have a burning desire to share, sharing buttons/popups/widgets must be right in front of them so you can instantly capitalize on this desire to share.

If you effectively create a desire to share and you place sharing channels well, you have a good shot at getting a large percent of your users to share. The important metric to watch here is share-rate. Share-rate is Number of People who Share/Number of People who Enter your App. Some viral apps we have built have had share-rates over 50%. This is good. Anything over 25% will give you significant viral traffic as long as your click-rate is good too.

Viral Index = Click-Rate * Share-Rate

It is that simple. Multiply these two numbers together and you will get a number usually between 0 and 2. If your viral index is greater than 1, your app will ‘go-viral’ with insanely huge traffic numbers. If it is less than 1, it will receive some multiplier in viral lift usually around 2x-10x.

A real example:

A Facebook app we built created a Newsfeed post for people to share with their friends. It had a Click-Rate of 4 clicks/post and a share-rate of 50%. 4*50% = 2 viral index.

This app went SUPER VIRAL and went from 0 users on Day 1, to 1 million users on Day 2, and 3 million users on Day 3.

Learn more behind the science of virality in this free webinar: The Secrets of Virality

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